Intrauterine growth in multiple pregnancies in relation to fetal number, chorionicity and gestational age

Abstract

Objectives

To examine birth weight in dichorionic and monochorionic twins and trichorionic triplets, and to estimate the relative independent importance on growth of fetal number, chorionicity and gestational age.

METHODS

Four groups of pregnancies were examined: 12 816 singleton pregnancies, 302 monochorionic twin pregnancies, 569 dichorionic twin pregnancies, and 97 trichorionic triplet pregnancies. Chorionicity was determined at 10–14 weeks on the basis of the presence or absence of the lambda sign in twins, and by examining the ipsilon zone in triplets. The relationship between birth weight and gestational age in singletons was established, and using this equation the expected mean birth weights for all gestational ages were calculated. For each case in all groups, the difference between the observed birth weight for each fetus and the appropriate normal mean for gestation in singletons was calculated (Z-score). Multiple regression analysis was used to examine the independent contribution of gestational age, number of fetuses and chorionicity in the prediction of actual birth weight and birth weight Z-score.